1. Field of the Invention
The present invention relates to a reflect array.
The present invention particularly relates to a polarization sharing reflect array and a frequency selective surface reflect array, including (1) a technique of scattering a TE (Transverse Electric) wave incident on a reflector in a direction different from that of regular reflection (specular reflection), (2) a technique of scattering both of a TE incident wave and a TM (Transverse Magnetic) incident wave in the same desired direction, (3) a technique of reflecting the waves only at a desired frequency and transmitting the waves at other frequencies, and (4) a technique which can direct a beam to a desired direction for an incident wave from any direction.
In addition, the present invention relates to a polarization independent control reflect array configured to receive a horizontally-polarized wave and a vertically-polarized wave incident from independently determined directions, and to scatter each of the polarized waves in a desired direction that can be independently determined.
Moreover, the present invention relates to a frequency sharing polarization independent control reflect array configured to perform control by causing array elements to act on horizontally-polarized and vertically-polarized waves coming in at different frequencies.
Moreover, the present invention relates to a reflect array which does not affect other systems, since the reflect array operates as if being invisible to electric waves at frequencies other than a desired frequency and thus transmits the waves.
Furthermore, the present invention relates to a reflect array used in a system configured to independently control two polarized waves: a horizontally-polarized wave and a vertically-polarized wave, such as polarization control MIMO, polarization diversity and sharing of broadcasting and communication.
2. Description of the Related Art
An example of a conventional reflect array is shown in F. Venneri, G. Angiulli and G. Di Massa, “Design of micro-strip reflect array using data from isolated”, IEEE Microwave and Optical Technology Letters, Vol. 34, No. 6, Sep. 20, 2002 (Non-patent Document 1). In the reflect array, as shown in FIG. 1, a shape of a micro-strip antenna is set as an array element and a metal flat plate is used as a ground plane. Moreover, dimensions “a” and “b” of the array element are determined by a phase difference as shown in FIG. 2.
However, the conventional reflect array as shown in FIGS. 1 and 2 has the following drawback because of the metal flat plate used as a back surface thereof. Specifically, electric waves at frequencies other than a desired frequency cannot be transmitted, polarized waves of a TM wave and a TE wave cannot be shared, and electric waves coming in from any direction cannot be radiated in a desired direction.
Moreover, the reflect array has the following drawback. Specifically, electric waves at frequencies other than a desired frequency cannot be transmitted, since the metal flat plate is used as the back surface thereof.
Furthermore, polarized waves independently incident from any directions cannot be radiated to any previously separately determined directions, since the reflect array does not even have a function of independently controlling horizontally-polarized and vertically-polarized waves.
Moreover, an example of a conventional frequency selective surface is shown in Junji Asada, “A Fundamental Study of Radar Absorber with Frequency Selective Surface”, Journal of Institute of Electronics, Information and Communication Engineers, Vol. J90-B No. 1, pp. 56-62, 2007. The frequency selective surface uses crossed dipoles as elements for a periodic structure to impart frequency selectivity.
Furthermore, the frequency selective surface has a drawback that a beam cannot be bent and scattered in a desired direction due to the absence of a structure to give a phase difference.
It is hard for the conventional reflect array and frequency selective surface to simultaneously realize any two or more of the following functions.
(1) Function of radiating a wave in a direction different from that of specular reflection.
(2) Function of radiating a TE incident wave and a TM incident wave both in the same desired direction.
(3) Function of reflecting waves at a desired frequency and to transmit waves at other frequencies.
(4) Function of directing a beam to a desired direction for an incident wave from any direction.
Moreover, the conventional reflect array is used as a reflector of a reflector antenna as described in the Non-patent Document 1, and a direction of arrival and polarization of an incident wave are determined by a primary radiator and thus are assumed to be previously known.
Therefore, no consideration has been given to a technique of scattering multi-path signals in a desired direction when the multi-path signals are incident on a reflector from any direction with any polarized wave by rotation in an outdoor propagation environment as described in Japanese Patent Application No. 2007-311649.
In addition, the conventional metal reflector only reflects incident waves, which come in as different polarized waves of horizontally-polarized and vertically-polarized waves, to a specular reflection direction, and does not have a function of independently controlling the polarized waves.
Moreover, the conventional reflect array and frequency selective surface do not have a function of independently controlling multiple polarized waves.
Furthermore, the reflect array does not have a frequency sharing polarization independent control function of independently controlling horizontally-polarized and vertically-polarized waves coming in at two different frequencies.